Władysław II Jagiełło was a significant historical figure who ruled as the King of Poland from 1386 to 1434. He was born around 1351 and was originally the Grand Duke of Lithuania. His marriage to Queen Jadwiga of Poland united the two nations, strengthening their political and military power in Eastern Europe. Jagiełło is best known for his role in the Battle of Grunwald in 1410, where his forces defeated the Teutonic Knights, a major military order. This victory marked a turning point in the struggle for dominance in the region and helped establish Poland-Lithuania as a powerful entity in Europe.